1. Field of the Invention
The present invention relates to the technique of multi-step charge pump.
2. Description of Related Art
A multi-step charge pump is used to, for example, change an input voltage into another input voltage, wherein the multi-step charge pump has multiple pumping levels, which can be pulled-up voltage levels or pulled-down voltage levels. In general, a multi-step charge pump is composed of a plurality of capacitors. In terms of a conventional multi-step charge pump, the output terminal thereof is electrically connected to a load to be driven; but for achieving a stable operation voltage, the load would be connected in parallel to an unchangeable capacitor and the unchangeable capacitor is termed as voltage-regulating capacitor.
FIG. 1 is a circuit diagram of a conventional charge pump. Referring to FIG. 1, a charge pump 100 is formed by two capacitors 102 and 104 and a voltage-regulating capacitor 106, wherein the voltage-regulating capacitor 106 is unchangeably in parallel connection with a load unit 120, and the voltage-regulating capacitor 106 together with the load unit 120 is connected between an output voltage Vo and a ground voltage. The capacitances of the capacitors 102 and 104 and the voltage-regulating capacitor 106 are respectively represented by C1, C2 and C3.
In the above-mentioned conventional charge pump composed of three capacitors, the capacitances thereof are, for example, the same, i.e., C1=C2=C3. The voltage-regulating capacitor 106 is connected to a grounded terminal all the time, and the terminals of other five capacitors are connected to an integrated circuit (IC). The pump is able to produce multiple voltages with different factors. FIG. 2 is a diagram showing various wiring circuits of the capacitors in the conventional charge pump of FIG. 1, wherein the wiring circuits produce a plurality of factors of voltage and the capacitors C1, C2 and C3 are subject to C1=C2=C3. Referring to FIG. 2, the charge pump herein is operated in two phases. The left circuits of the dotted lines are operated in charging-phase, and the right circuits of the dotted lines are operated in output-phase, wherein there are four factors of voltage: triple (3×), double (2×), one and a half times (1.5×), and half (0.5×) which are produced respectively by the circuits of FIGS. 2(a), 2(b), 2(c) and 2(d).
In FIG. 2(a), the conventional charge pump requires a capacitor unchangeably as the voltage-regulating capacitor and the capacitor 106 unchangeably serves as the voltage-regulating capacitor of an output voltage Vo. During the charging-phase, the capacitors 102 (C1) and 104 (C2) are charged by an input voltage Vin so as to make 102 and 104 store Vin. During the output-phase, the connection between the capacitors 102 and 104 is switched to serial connection, and the input voltage Vin is connected in series to a negative voltage terminal and another terminal thereof is connected to a voltage output terminal, so that Vo is boosted to a voltage three times greater than the voltage Vin. In FIG. 2(b), the capacitor 106 still serves as the voltage-regulating capacitor of Vo. During the charging-phase, the capacitor 102 (C1) is charged by Vin to store the voltage Vin; meanwhile, Vin is connected to the negative voltage terminal of the capacitor 104 (C2). Another terminal of the capacitor 104 (C2) is connected to the output terminal so as to boost Vo to a voltage double of the voltage Vin. During the output-phase, the capacitor 104 (C2) is charged by the input voltage Vin so as to make the capacitor 104 (C2) store Vin; meanwhile, Vin is connected to the negative voltage terminal of the capacitor 102 (C1). Another terminal of the capacitor 102 (C1) is connected to the output terminal so as to boost Vo to a voltage double of the voltage Vin. In FIG. 2(c), the capacitor 106 (C3) unchangeably serves as the voltage-regulating capacitor of Vo. During the charging-phase, the capacitors 102 and 104 in series connection are charged by Vin so as to make both capacitors store voltage of 0.5 Vin. During the output-phase, Vin is connected to the negative voltage terminal of the circuit formed by the capacitors 102 and 104 in parallel connection. Another terminal of the parallel circuit is connected to the output terminal to boost Vo to a voltage of 1.5 Vin. In FIG. 2(d), the capacitor 106 (C3) still unchangeably serves as the voltage-regulating capacitor of Vo. During the charging-phase, the capacitors 102 and 104 in series connection are charged by Vin to store the voltage of 0.5 Vin. During the output-phase, Vin is connected to the positive voltage terminal of the circuit formed by the capacitors 102 and 104 in parallel connection. Another terminal of the parallel circuit is connected to the output terminal to down push Vo to the voltage of 0.5 Vin. The factors of voltage produced by the pump are fixed and thus unchangeable to meet the user demand.
FIG. 3 is a diagram of showing various wiring circuits of the capacitors in another conventional charge pump. Differently from FIG. 2, the capacitances C1, C2 and C3 of three capacitors 102 that 104 and 106 in FIG. 3 are subject to C1:C2:C3=a:b:c, and a≠b≠c; thus, the charge pump in FIG. 3 can produce multiple voltages in different factors. Similarly to the circuits of FIGS. 2(a) and 2(b), the circuits of FIGS. 3(a) and 3(b) can respectively produce a triple voltage and a double voltage. In FIG. 3(c), the capacitor 106 (C3) unchangeably serves as the voltage-regulating capacitor of Vo. During the charging-phase, the capacitors 102 (C1) and 104 (C2) in series connection are charged by Vin so as to make the capacitor 102 store voltage of [b/(a+b)]×Vin and the capacitor 104 store voltage of [a/(a+b)]×Vin. During the output-phase, Vo=Vin−[b/(a+b)]×Vin+[a/(a+b)]×Vin=[2a/(a+b)]×Vin. In FIG. 3(d), the capacitor 106 still unchangeably serves as the voltage-regulating capacitor of Vo. During the charging-phase, the capacitors 102 (C1) and 104 (C2) in series connection are charged by Vin so as to make 102 (C1) store the voltage of [b/(a+b)]×Vin and the capacitor 104 (C2) store the voltage of [a/(a+b)]×Vin. During the output-phase, Vo=Vin+[b/(a+b)]×Vin−[a/(a+b)]×Vin=[2b/(a+b)]×Vin. The charge pump of FIG. 3 is able to adjust the capacitance ratio between the employed capacitors according to the desired factor of voltage.
FIG. 4 is a circuit diagram of yet another conventional charge pump. Referring to FIG. 4, the charge pump 100 is an enhanced one of FIG. 1, where a capacitor 108 is additionally employed for producing more pumping levels. The employed four capacitors 102, 104, 106 and 108 have the same capacitances, i.e., C1=C2=C3=C4, wherein the voltage-regulating capacitor 106 (C4) serves as the voltage-regulating capacitor and a terminal thereof is connected to a grounded terminal all the time, and the rest seven terminals of the capacitors 102, 104, 106 and 108 are connected to an IC. The charge pump herein is able to produce multiple voltages with different times, such as quadruple (4×), triple (3×), two and a half times (2.5×), double (2×), one and a half times (1.5×), 1.66 times (1.66×), 1.33 times (1.33×), 0.66 times (0.66×), a half (0.5×) and 0.33 times (0.33×).
FIGS. 5A-5B are diagrams showing various switching circuits respectively for a factor in the conventional charge pump 100 of FIG. 4. In FIG. 5A(a), the capacitor 106 (C4) unchangeably serves as the voltage-regulating capacitor of an output voltage Vo. During the charging-phase, the capacitors 102 (C1), 104 (C2) and 108 (C3) in parallel connection are charged by an input voltage Vin so as to make them store Vin. During the output-phase, Vin is connected to the negative voltage terminal where the capacitors 102 (C1), 104 (C2) and 108 (C3) are connected in series to and another terminal thereof is connected to a voltage output terminal, so that Vo is boosted to a voltage of 4 Vin. In FIG. 5A(b), the capacitor 106 (C4) still serves as the voltage-regulating capacitor of Vo. During the charging-phase, the capacitors 102 (C1), 104 (C2) and 108 (C3) are charged by Vin to store the voltage Vin. During the output-phase, the capacitors 102 (C1) and 104 (C2) are connected in parallel to each other, followed by connecting in series them to the capacitor 108 (C3). Vin is connected to the negative voltage terminal of the capacitors 102 (C1) and capacitor 104 (C2) in parallel connection, and another terminal thereof is connected to the output terminal so as to boost Vo to a voltage of 3 Vin. In FIG. 5A(c), within the charging-phase, the capacitors 102 (C1), 104 (C2) and 108 (C3) are charged by Vin so as to make the capacitor 108 (C3) store a voltage of Vin, and the 102 (C1) and 104 (C2) store a voltage of 0.5 Vin. During the output-phase, the capacitors 102 (C1) and 104 (C2) are connected in parallel to each other, followed by connecting in series them to the capacitor 108 (C3). Then, Vin is connected to the negative voltage terminal of the capacitors 102 (C1) and capacitor 104 (C2) in parallel connection, and another terminal thereof is connected to the output terminal so as to boost Vo to a voltage of 2.5 Vin. In FIG. 5A(d), within the charging-phase, the capacitors 102 (C1), 104 (C2) and 108 (C3) are charged by Vin to store a voltage of Vin. During the output-phase, Vin is connected to the negative voltage terminal of the capacitors 102 (C1), capacitor 104 (C2) and capacitor 108 (C3) in parallel connection, and another terminal thereof is connected to the output terminal so as to boost Vo to a voltage of 2 Vin. In FIG. 5A(e), within the charging-phase, the capacitors 102 (C1), 104 (C2) and 108 (C3) are charged by Vin to make the capacitor 108 (C3) store a voltage of Vin and the capacitors 102 (C1) and 104 (C2) store a voltage of 0.5 Vin. During the output-phase, Vin is connected to the positive voltage terminal of the capacitors 102 (C1) and capacitor 104 (C2) in parallel connection, followed by connecting in series them to the negative terminal of the capacitor 108 (C3); another terminal thereof is connected to the output terminal so as to boost Vo to a voltage of 1.5 Vin. In this way, by properly wiring the circuit of the capacitors, other pumping levels can be produced. The circuits of FIGS. 5A(f), 5B(g), 5B(h), 5B(i) and 5B(j) respectively produce 1.66 Vin, 1.33 Vin, 0.66 Vin, 0.5 Vin and 0.33 Vin, and these are well known for anyone skilled in the art and omitted to describe.
A conventional charge pump requires an unchangeable capacitor as a voltage-regulating capacitor corresponding to a load. With the conventional charge pump, several external capacitors with the same capacitance are used; therefore, the produced voltage combinations are fixed and unable to be changed to obtain an optimal factor of voltage for different applications, which may results in a poor efficiency for some application voltages.